Ectotherms (including marine turtles) being especially sensitive to climate, are at risk to the accelerated rate of human-driven climate change. This study addresses two concerns associated with marine turtles and climate change – the relationship between the timing of marine turtle nesting and sea surface temperature; and the concern over the feminization of marine turtle populations due to rising sand temperatures. Previous studies of loggerhead sea turtles (Caretta caretta) and green sea turtles (Chelonia mydas) have documented the relationship between sea surface temperatures and nesting phenology. Earlier nesting behaviors in both species have been associated with warmer sea surface temperatures. Also, sex determination for marine turtles is temperature-dependent. Due to current sand temperatures, it is estimated that loggerhead (Caretta caretta) nests along the Atlantic coast of Florida already produce over 89% female hatchlings. Using shade to reduce nest temperature and increase the proportion of male hatchlings is one option for mitigating the impacts of climate change on marine turtle sex ratios. In this study, a 21- year (1988-2008) dataset of hawksbill sea turtle (Eretmochelys imbricata) nesting at Buck Island Reef National Monument, St. Croix, U. S. Virgin Islands was analyzed in a similar manner to previous studies. It was found that warmer sea surface temperatures were associated with longer nesting seasons and later median nesting dates. Additionally, a preliminary sand shading study was conducted in the first field season (2011) with a subsequent loggerhead nest shading study in the following field season (2012). Although hatching success was not significantly impacted, temperatures were significantly reduced in the majority of shaded nests. This practice may not be immediately applicable as a means of managing sex ratios, but it could be used to reverse the temperature effects of nest relocation

No description available.

The methods of sex determination through skeletons or through objects in graves has been used on and off since the nineteenth century. Most of the osteological methods are however developed on intact bones, and the archaeological method assume that jewelry is female associated and weapons are male associated. A tendency to choose the archaeological sex determination above the osteological sex determination can be spotted as well. The study examines how the osteological sex determination methods could be used on fragmented skeletal remains, and question the archaeological sex determination method with a gender perspective. This will be achieved by analyzing thirteen graves from a burial ground in Lekarehed, Lärbro parish (socken), Gotland. The skeletal remains were excavated in 1878 and 1951 and is dated to late Bronze age–early Iron age and the Viking age. The aim with this study is to get a deeper understanding of how the methods can be used, and to shed light on the stereotypical view on femininity and masculinity that exists. The aim is also to emphasize that the most important and most interesting information comes from the discussion of the problems that exist in these methods, and that the most important thing is not to decide what is feminine or masculine, or to choose one method in front of the other. The analysis resulted in one certain, four uncertain and eight graves without sex determination regarding the osteological method, and two certain, one uncertain and ten graves without sex determination regarding the archaeological method. In the discussion, the problems with putting the woman and the man as pairs of opposition is brought up, because it excludes the graves that cannot be put in one of these two categories. The objects in the graves can represent something other than sex as well, for instance age or status. The cooperation between the osteologist and the archaeologist is important for the knowledge to evolve and to carry on. By looking at the material in a new way, new insights will perhaps come forth. / Denna uppsats handlar om hur det går att använda osteologiska och arkeologiska könsbedömningsmetoder på ett fragmenterat skelettmaterial. Metoderna som används för den osteologiska könsbedömningen är ofta, om inte alltid, utvecklade på intakta ben, och när det gäller fragmenterade ben blir könsbedömningen svårare att utföra. Den arkeologiska könsbedömningen är en könsbedömning gjord via föremålen i gravar och utgår kortfattat ifrån att vapen är manliga och smycken är kvinnliga. Den granskas här genom ett genusperspektiv som ifrågasätter synen på kvinnligt och manligt och hur de tankarna överförs till forntiden. Det finns också problematik i hur osteologin och arkeologin stämmer överens med varandra. För att undersöka problematiken har ett skelettmaterial på 13 gravar från ett gravfält i Lekarehed, Lärbro socken, Gotland analyserats. Resultatet för den osteologiska könsbedömningen blev en säker, fyra osäkra kön och åtta stycken utan könsbedömning. Resultatet för den arkeologiska könsbedömningen blev två säkra, en osäker och tio utan en könsbedömning. Slutsatserna i uppsatsen är att de osteologiska och arkeologiska könsbedömningsmetoderna blev problematiska. Den osteologiska på grund av de fragmenterade benen och svårigheter inom den morfologiska metoden. Den arkeologiska på grund av att det inte fanns könsindikerande föremål i många gravar och även på grund av vad vi sätter in i kvinnligt och manligt associerade föremål. Där både en osteologisk och en arkeologisk könsbedömning fanns, stämde de överens med varandra. Det betyder dock inte att de inte ska problematiseras, eftersom vi inte vet om forntidens människor tyckte att smycken var kvinnliga och vapen var manliga. Vi vet inte heller om föremålen representerar kön, eller vad föremålen hade för användningsområde. Det blir också svårt att dra slutsatser om hur individerna i Lekarehed såg på kvinnligt och manligt, eftersom resultaten av könsbedömningarna i många fall var bristfälliga, och för att gravfältet representerar olika tidsperioder. Ny kunskap kan uppkomma om vi slutar att sätta kvinnan och mannen som motsatspar, och är öppna för en annan syn på genus som inte representerar dagens (västerländska) samhälle, eftersom de gravarna som hamnar utanför de två kategorierna blir osynliga. Det är viktigt att osteologen och arkeologen samarbetar, och inte väljer den ena metoden framför den andra, eftersom den mest intressanta informationen och kunskapen kommer utifrån diskussionen av problematiken, och vilka nya aspekter som kan tillföras om vi inte förutsätter att forntidens människor såg på kvinnligt och manligt på det sättet som det finns en tendens till idag.

Much of what we know about temperature-dependent sex determination (TSD) in reptiles stems from constant temperature incubation studies in the laboratory. In recent years, as TSD studies moved into the field it became evident that TSD was much more complex than previously thought. The present study attempted to reveal the complexity of TSD, as it relates to other features of the species' biology and physical characteristics tractable only in the field, such as fluctuations in incubation temperature and reproductive life history. To this end I studied the ecology of the turtle Carettochelys insculpta, a TSD species inhabiting the wet-dry tropics of northern Australia from 1996 to 1998. I tested hypotheses associated with movements, activity, behaviour, reproduction, nest site choice, nest temperatures, embryonic survival, embryonic aestivation, hatch-ling sex ratios, and emergence in the species. Each of these was also considered in the context of the influence of the wet-dry tropics. Compared to other turtles inhabiting lotic habitats, C. insculpta occupied considerably larger home ranges, covering up to 10 km of river. Of previously published factors influencing home range size, low productivity of the (micro) habitat may best explain the extensive home ranges in C. insculpta. Patchiness and low nutrient value of the chief food (aquatic vegetation) of C. insculpta may force turtles to cover large expanses of river to acquire sufficient energy for growth and reproduction. Females were more active, moved farther, and occupied larger home ranges than males. Home ranges of females comprised 1-4 activity centres, many of which were associated with thermal springs. I suggest that females may exhibit increased activity and movements relative to males because of sexual inequality in parental investment, where food is particularly limiting (e.g., in species with biennial reproduction). Biennial reproduction in the population allowed the examination of the influence of reproductive condition on home range size, movements, and activity. Reproductive condition did not influence home range or activity, but gravid turtles moved father between successive sightings than non-gravid females. Individual data corroborate these findings, with females moving farther between successive sightings while gravid compared to while spent. Contrary to previous reports, turtles did not appear to move into estuarine areas or lowland flood plains during the wet season, but moved into the riparian forest and possibly into wetlands adjacent to the main channel in the vicinity of their dry season home ranges. During the study I documented the turtles' use of small, localized thermal springs discharging from the river bottom. Dataloggers attached to the carapace to monitor ambient water temperatures recorded the frequency and duration of thermal spring use by individuals. Turtles used the thermal springs frequently during the winter (4-6 months) when river temperatures were lower than that of the thermal springs (8 = 29 � 0.52� C). Turtles often utilized thermal springs for several consecutive hours, leaving the springs only to surface for air. Thermal springs may be derived from ground water (which maintains a temperature equivalent to the annual mean air temperature), rather than from a specific geothermal heat source. Nine of 19 radio-telemetered adult females were seen to use thermal springs, of which seven were gravid and two non-gravid. Thus, gravid turtles may seek thermal springs more than non-gravid turtles. Frequency, duration, and timing of usage collectively suggest active thermoregulation as the primary function of thermal spring use. Utilization of thermal springs probably permits turtles to be more active in cooler months, which may enhance growth rates and accumulation of energy for reproduction. Onset of nesting along river stretches with thermal springs preceded nesting in a stretch not known to have thermal springs by 24 days. Thus, I speculate that by warming themselves on thermal springs in the months prior to nesting, turtles may have accelerated follicular development and nested earlier. Female C. insculpta matured at ca. 6 kg body mass (38.0 cm carapace length, 30.5 cm plastron length). Turtles produced egg sizes and clutch sizes similar to that of other turtle species of similar size. Turtles reproduced every second year, but produced two clutches in each breeding year, ca. 40 days apart. Thus, it appeared that females were energy limited, possibly due to the low available energy content of the dry season diet (aquatic vegetation). Life history theory predicts that if some costly behaviour is associated with reproduction, skipping years could reduce that cost and allow savings to be directed into future reproduction. The present study revealed no obvious accessory behaviour in the population. Within years, clutch mass did not differ between early (first) and late (second) clutches. However, earlier clutches tended to have more and smaller eggs per clutch but than later clutches, a new finding for turtles that has been demonstrated in lizards and other animals. Because the study spanned both years with 'big' and 'small' wet seasons, I was able to examine how the magnitude of the wet season influenced reproductive characteristics. Following big wet seasons turtles produced larger, heavier, and more eggs per clutch than they did after small wet seasons. Relationships among body size, egg size, and clutch size were evident after two big wet seasons but not apparent after two small wet seasons. Collectively, annual variation in reproductive characteristics and current life history theory suggest that a big wet season is a plentiful time for the turtles. I investigated beach selection of nesting pig-nosed turtles (Carettochelys insculpta) along a 63 km stretch of river in 1997 and 1998. I used three classes of beaches to examine beach choice: beaches with nests, beaches with only crawls, andbeaches without nests or crawls. Across these beach types I compared aspect, solar exposure, temperature, substrate moisture, height, water depth at approach, and the height of cohesive sand. I located 82 nesting beaches with 221 nests, and identified 171 potential nesting beaches based on previously published criteria. Beaches with nests had a greater substrate moisture content and corresponding higher cohesive sand line (hereafter CSL) than beaches without nests. Beaches with nests also had a higher CSL than beaches with only crawls. Apparently, turtles could not excavate a nest chamber above the CSL due to loose substrate consistency causing sand to fall in on itself. Turtles could only nest at low elevations below the CSL on beaches with lower substrate moisture. Turtles apparently avoided nesting on these beaches due to the higher probability of nest flooding, as corroborated by a concurrent study. Beach temperatures increased with a seasonal increase in air temperatures, and were influenced by aspect and total angle of solar exposure. Temperatures did not differ among beaches with nests, beaches with only crawls, and beaches without crawls or nests. Therefore, there was no indication that turtles were manipulating offspring sex through choice of nesting beach. However, turtles may be manipulating sex by nesting in areas with particular thermal characteristics within beaches. Two related aspects of hatchling emergence were studied. Using emergence phenology data, nest temperatures, historical weather data, and a developmental model, I tested the hypothesis that delayed hatching occurred in C. insculpta, and that such a delay would allow hatchlings to time their emergence to match the onset of the wet season. Hatchling C. insculpta emerged, on average, 17 days later than dates predicted from a developmental model. Combined with observations of hatchlings remaining in eggs until emergence, these results confirmed delayed hatching in nature. This delay was synchronized with initial river rises associated with the onsetof wet season rains, and is consistent with published criteria for embryonic aestivation. On a diel scale, I generated predictions of two potentially competing models for nocturnal emergence in hatchling turtles, based on the knowledge that air temperatures decrease with season during the emergence period. A test of those predictions for C. insculpta produced ambiguous results. However, further analysis indicated that C. insculpta, and probably other nocturnally emerging turtle species, respond to a decline in diel temperature rather than an absolute temperature. The former would ensure nocturnal emergence, while the latter is experienced during the day as well as at night. Nocturnal emergence may be associated with nesting in open microhabitats. The 'decision' of when and where to nest can influence both offspring survival and hatchling sex ratios in animals with temperature-dependent sex determination (TSD). Knowledge of how these maternal attributes influence the incubation environment is an important first step in hypothesizing why TSD evolved in a particular species. 1 studied the influence of nest site choice and timing of nesting on embryonic survival and hatchling sex ratios. Predation and flooding were the major sources of embryonic mortality. Embryonic survival was influenced by both lay date and nest site choice: In one year when nesting began later, nests laid later and at lower elevations were destroyed by early wet season river rises. In other years early nesting precluded flood mortality. However, turtles did not nest at the highest available elevations. I hypothesized that turtles were unable to nest at higher elevations because the sand was dry and not cohesive. A field experiment demonstrated that turtles were constrained to nest at lower elevations where they could construct a nest chamber. A mathematical model predicting hatchling sex from fluctuating temperatures was applied to temperature data from 102 natural nests. Resultsconfirmed a type la pattern of TSD, whereby males are produced from cooler temperatures and females from warmer temperatures. The principal determinant of hatchling sex was lay date. Clutches laid earlier in the season produced mainly males, while later clutches yielded mostly females, due to seasonal ramping of air and sand temperatures. However, nest site choice also exerted an influence on hatchling sex. Female-producing clutches were deposited at higher elevations than male-producing clutches. The onset of nesting was not influenced by water temperatures, but may have been related to the magnitude of the previous wet season(s). Turtles nested earlier after two 'big' wet seasons and later following two 'small' wet seasons. This pattern indicates that the wet season is a plentiful time for the turtles. Adaptive 'differential fitness' models for the evolution of TSD have recently been reviewed and clarified. The differential fitness model that best fits C. insculpta is the 'timematching' model, whereby one sex benefits more than the other from early hatching. Male C. insculpta hatched 2-3 weeks earlier then females, on average. Benefit to early hatching males and, therefore, the ultimate selective mechanism (e.g., growth, time to mature) is unknown. Obtaining such data will likely prove difficult in such a long-lived species. A recent adaptive explanation for the evolution and maintenance of temperaturedependent sex determination (TSD) in reptiles rests upon the assumption that mothers can predict or manipulate offspring sex. I postulated that four physiological and behavioural criteria must be met in order for this assumption to be valid: (1) a strong correlation must exist between substrate temperatures during nest site choice and nest temperatures during the period of development when sex is determined in the egg (thermosensitive period = TSP). (2) Assuming that (1) is possible, mothers would need to be capable of correcting for temporal factors obscuring the predictable thermalcharacteristics of nest sites. This could be accomplished in two ways. By contracting nesting times mothers could assess the relative temperatures of alternate nest sites with some accuracy. A protracted distribution of nesting times could greatly reduce a mother's ability to distinguish between, for example, a cooler nest site at a warmer time and a warmer nest site at a cooler time. Alternatively, mothers would need to be able to incorporate temporal changes in nest site temperatures. (3) Sufficient variation in thermal profiles among nest sites, relative to the breadth of temperatures producing both sexes (pivotal temperatures), would be necessary. For example, if most nests produced both sexes, then depth of the eggs would be the deciding factor determining sex, leaving little opportunity for nest site choice to produce one sex or the other. (4) Mothers would need access to nest sites spanning a range of thermal profiles in order to produce either offspring sex. To this end, home range size relative to the number and location of nesting beaches should be important. I tested these four predictions in Carettochelys insculpta, a beach nesting turtle with TSD, using three years of field data on nest site choice, nesting times, thermal characteristics of nests, hatchling sex ratios, and movements of nesting turtles. A strong positive correlation existed between assessable substrate temperatures at nest site choice and mean daily TSP temperatures in all three years. However, the proportion of explained variation was highly variable among years, and low in 1998. Accordingly, the proportion of nests in which substrate temperatures at nest site choice predicted offspring sex correctly was low in 1998 (48- 62 %, depending on treatment of the data). Nesting times were normally distributed, and combined with diel changes in nest site temperatures greatly reduce a turtle's ability to distinguish between sites that would produce different sexes. Considerable among-clutch variation in thermal profiles to produce variable sex ratios existed, agreeing with other studies on turtles. Radiotelemetry indicated that home rangesencompassed several nesting beaches with differing thermal profiles, indicating scope for producing the desired sex. However, the seasonal increase in air temperatures resulted in an overriding effect of mostly males being produced in early (first) clutches and mainly females being produced in late (second) clutches. Collectively, the results suggest that C. insculpta mothers would find it difficult to predict, and therefore, manipulate hatchling sex, supporting the conventional notion that TSD mothers have little or no control over offspring sex.

Monoecy, the production of distinct male and female flowers on the same plant, is an important, though little studied, sexual strategy in the rainforest understory. This study of a monoecious plant discovered a cue to induce flowering, explored the interplay of gender constraint vs. plasticity in a natural population, and tested possible causes of gender in two laboratory experiments. An experiment in the lab found that reduced photoperiod for three weeks is an unambiguous cue for flowering. The remarkably long inductive period is followed by a long and variable period of floral initiation. This results in only partial synchronization of flowering among plants in a patch, which enhances mating opportunities in this protandrous plant. Inflorescence architecture is highly constrained, and ideally produces a phenotypic gender (proportion female) of about 0.5. However, in the forest at Las Cruces, Costa Rica, most plants were less female than predicted, mostly through abortion of female buds. Plants showed gender plasticity between and within years. Large plants produced more flowers and were more female in gender, and less variable in gender, than small plants. Reproduction was poorly correlated with environmental resource availability, measured as canopy openness, soil moisture, pH, and soil phosphorus, ammonium and nitrate. Phenotypic selection analysis on seed production suggests an optimal gender of 50-60% female, yet plasticity to be less female than this optimum, and in particular to express only male function, has been maintained. In a factorial experiment in the lab, high light or high nitrogen caused plants to produce more flowers and to be proportionally more female, and larger in weight, than low light or nitrogen. The effects of light and nitrogen on reproduction, plant size, and leaf greenness suggest an energy based determination of gender. Gender may be mostly influenced by plant size, but sometimes also opportunistically by environment. Inoculation with mycorrhizas caused plants to be less female in gender, and smaller in weight, than plants that were not inoculated. This suggests a net cost of mycorrhizas under experimental conditions, and supports the emerging view of the mycorrhizal symbiosis as not necessarily mutualistic under all circumstances.

The molecular mechanism of complementary sex determination in the haplodiploid organisms is poorly understood and has only been described in the honeybee Apis mellifera. In the haplodiploid system, males develop from unfertilized eggs and females from fertilized eggs. However, in some rare cases, diploid males develop from fertilized eggs. They can be distinguished from diploid and haploid males at the molecular level since they are heterozygous like females but are homozygous, like haploid males, at the sex determination locus. In this project, Osmia bicornis was chosen as the model organism, and the aim is to identify the complementary sex determination locus which should be homozygous in all diploid males. Bee nests were collected from the bees' natural habitat, and potential diploid males were identified. Data analysis of whole-genome sequencing on 17 potential diploid males was performed, which identified 80 candidate sex determination loci with 259 genes. Homologs of the Csd gene in A. mellifera were identified but not found in any candidate complementary sex determination loci.

Sex determination among reptiles is a very variable matter across it's taxa. We meet there temperature sex determination and genotypic sex determination with many independent transitions between them. It is a group suitable to study evolution of sex determination, sex chromosomes and sex determination genes. Rare cases of sex reversal caused by extreme incubation temperature or exogenous hormones have been reported in recent years. In case of Acrodont lizard, Pogona vitticeps, was reported sex reversal caused by high incubation temperatures. Our purpose was to repeat the experiment, mainly due to insufficient conclusiveness of used methods. We wanted to expand the experiment by hormonal reversal, studying persistence of sex reversal to maturity and fertility of reversed individuals. We managed successfully to demonstrate sex reversal in both treatments by histological examination. Individuals with discordant phenotypic and genotypic sex were breed till one year of life, which demonstrate persistence of reversal. Our outcomes are concordant with most recent work on this species and show full functional phenomenon of sex reversal with reptiles, which studying could contribute to our understanding of evolution of sex determination.

Les téléostes, le clade possédant le plus d’espèces parmi les vertébrés, emploient une saisissante diversité de mécanismes de détermination du sexe, incluant des mécanismes génétiques et environnementaux. Des études récentes ont identifié de nombreux nouveaux régulateurs génétiquesdu développement sexual des poissons et ont introduit la notion de “terrain de jeux évolutif”. Le but de ce projet de thèse est de donner une vue complète des dynamiques évolutives des déterminants du sexe dans un ordre de téléostes, les Esociformes. Dans notre espèce focale, Esox lucius, nous avons identifié une duplication d’un membre de la famille des TgfB – une famille qui a émergé en tant que fondamentale dans la régulation du sexe chez les téléostes – comme MSD (gène controlant la détermination du sexe). Nous avons obtenu des preuves fonctionnelles du rôle de ce gène en tant que MSD, de son interaction avec des facteurs environnementaux, ainsi que des nouvelles informations sur les processus évolutifsCe gène est perdu dans une population de la même espèce en Amérique du Nord, mais il est conservé parmi les autres Esociformes. En parallèle, d’autres systèmes de détermination du sexe ont été identifiés dans des espèces proches. De plus, dans des clades plus distants comme Umbra et Dallia, le MSD d’Esox n’est pas présent, et d’autres mécanismes implicants de nouveaux MSD ont été identifiés, complefixiant l’histoire évolutive des MSD dans ce groupe, qui reflète la plasticité génétique observée dans les téléostes en général. / Teleost fishes, the most species-rich clade among vertebrates, employs an astonishing diversity of sex-determining (SD) mechanisms, including environmental and genetic systems. Recent studies identified many new genetic regulators in fish sexual development that lead to the notion of an 'evolutionary playground'.This thesis project aims to provide a complete picture of the evolutionary dynamic of SD systems within a small order of teleost, Esociformes. In our focal species Esox lucius, we idenWhile the gene is lost in another population of the same species rapidly possibly during post-glacial recolonization process, it is well conserved among different species. Meanwhile, additional transition of SD system have also been identified in a sister Esox species. Moreover, in the most distant genera Dallia and Umbra, the Esox master SD gene is not present and we found different SD mechanisms with novel SD genes that adds additional layers of complexity to this group, which mirrors the observed high genetic plasticity in teleost SD

No description available.

<p>Understanding transcriptional regulation in development and disease is one of the central questions in modern biology. The current working model is that Transcription Factors (TFs) combinatorially bind to specific regions of the genome and drive the expression of groups of genes in a cell-type specific fashion. In organisms with large genomes, particularly mammals, TFs bind to enhancer regions that are often several kilobases away from the genes they regulate, which makes identifying the regulators of gene expression difficult. In order to overcome these obstacles and uncover transcriptional regulatory networks, we used an approach combining expression profiling and genome-wide identification of enhancers followed by motif analysis. Further, we applied these approaches to uncover the TFs important in mammalian sex determination.</p><p>Using expression data from a panel of 19 human cell lines we identified genes showing patterns of cell-type specific up-regulation, down-regulation and constitutive expression. We then utilized matched DNase-seq data to assign DNase Hypersensitivity Sites (DHSs) to each gene based on proximity. These DHSs were scanned for matches to motifs and compiled to generate scores reflecting the presence of TF binding sites (TFBSs) in each gene's putative regulatory regions. We used a sparse logistic regression classifier to classify differentially regulated groups of genes. Comparing our approach to proximal promoter regions, we discovered that using sequence features in regions of open chromatin provided significant performance improvement. Crucially, we discovered both known and novel regulators of gene expression in different cell types. For some of these TFs, we found cell-type specific footprints indicating direct binding to their cognate motifs.</p><p>The mammalian gonad is an excellent system to study cell fate determination processes and the dynamic regulation orchestrated by TFs in development. At embryonic day (E) 10.5, the bipotential gonad initiates either testis development in XY embryos, or ovarian development in XX embryos. Genetic studies over the last 3 decades have revealed about 30 genes important in this process, but there are still significant gaps in our understanding. Specifically, we do not know the network of TFs and their specific combinations that cause the rapid changes in gene expression observed during gonadal fate commitment. Further, more than half the cases of human sex reversal are as yet unexplained. </p><p>To apply the methods we developed to identify regulators of gene expression to the gonad, we took two approaches. First, we carried out a careful dissection of the transcriptional dynamics during gonad differentiation in the critical window between E11.0 and E12.0. We profiled the transcriptome at 6 equally spaced time points and developed a Hidden Markov Model to reveal the cascades of transcription that drive the differentiation of the gonad. Further, we discovered that while the ovary maintains its transcriptional state at this early stage, concurrent up- and down-regulation of hundreds of genes are orchestrated by the testis pathway. Further, we compared two different strains of mice with differential susceptibility to XY male-to-female sex reversal. This analysis revealed that in the C57BL/6J strain, the male pathway is delayed by ~5 hours, likely explaining the increased susceptibility to sex reversal in this strain. Finally, we validated the function of Lmo4, a transcriptional co-factor up-regulated in XY gonads at E11.6 in both strains. RNAi mediated knockdown of Lmo4 in primary gonadal cells led to the down-regulation of male pathway genes including key regulators such as Sox9 and Fgf9. </p><p>To find the enhancers in the XY gonad, we conducted DNase-seq in E13.5 XY supporting cells. In addition, we conducted ChIP-seq for H3K27ac, a mark correlated with active enhancer activity. Further, we conducted motif analysis to reveal novel regulators of sex determination. Our work is an important step towards combining expression and chromatin profiling data to assemble transcriptional networks and is applicable to several systems.</p> / Dissertation